shorter gearing options for a 901 box?

givory · 05-15-2006, 05:35 PM

I have a 901 gearbox behind a 2L six powered 914 vintage racer.
I recently switched from 205/50x15 tires to 205/60x15 to comply with rules, leaving my gearing way too tall, even for a fast track [can't get into 5th gear].

I've done the "flip-3-and-5-replace-4-with-an-S-gear" trick. What are my options from here [with a reasonable cost]? I have the regular 7:31 R&P. How about the 8:31 [?] R&P? Roughly how much and who sells them? Or should I start again with a full new gear set, 3rd through 5th? Any suggestions on which combinations have worked for racers on a beer budget?

Thanks,
Gavin Ivory

jluetjen · jluetjen's Garage

The 8:31 is a 915 gearbox option, not a 901/911. I'd keep an eye on ebay and you can most likely score a 901/911 box with different ratios then what you have now. Combine the two of them and you'll most likely come out pretty good. That's what I'm doing. I've got an aluminum 901 in the car now, and I bought a 914 and a 911 gear box. Between them I've got most of the gears that I want, or I'm only off by a tooth or two.

I made an excel spreadsheet with the different ratios that I have and want, as well as the road speed for every 500 RPM. Then I picked the gears that I wanted and tracked them down.

trekkor · 05-15-2006, 07:25 PM

M-S-X.

I like it a lot...

My 2.0 SIX engine revs to 7300rpms if I ask it to, so my rpms into 3rd, 4th and 5th start at 4800, 5200 and 5700 rpms hard upshifting. Really good for the track. I haven't seen the top of 5th yet, which would be around 130mph.

The "K" 3rd gear might get you onto the power band a little faster, but down shifting into it might be rough. ( might )

KT

givory · 05-16-2006, 03:59 AM

Excellent help - thanks. No R&P options, I guess. But I have a spare 901 with stock gears in good shape ... perhaps I'll just hunt for the gears.
Gavin

ErVikingo · 05-16-2006, 06:44 AM

Gavin,

I have an R/P for 901 which will give you lower gearing. I also have a detailed spreadsheet with all options. email me for details.

Juan

John Rogers · 05-16-2006, 12:46 PM

I run K-Q-V for the top three gears. I used to have M-S-X but with the six I found that the X was even too high as we max out at 7400 RPM or so at a highspeed track such as the CA Speedway on the NASCAR portion. I think top speed on the var will be the same due to HP and drag so the slightly lower gearing helps get there a tad faster. This is what Jim Patrick and Wayne Baker recommend as far as I know for their vintage 2L cars.

Brant · 05-16-2006, 01:09 PM

with your tall sidewalls you will want to go pretty low.
but low is not cheap...

most of the 60 guys with 60 series tires, run JOS for their gear box on vintage 2.0/6 cars...

JOS is pretty pricey though
I think the J is going for big money
(although I desperately want one for little money if anybody happens to have a spare out there?)

brant

Vintage911Racer · 05-16-2006, 01:31 PM

I guess the main question is how high do you want to rev the motor? I run mine to 8K all the time and I run a K, Q, V... That seems to be a good all around setup... I think W may be too tall but I also dont know the tracks you are running on.

J, O, S is a good short box
K, Q, V good all around box.

givory · 05-16-2006, 02:05 PM

...this is really great help!

Juan - I will PM you re the R&P .. thanks.

Though my engine is built to run higher, I limit it to 7,200 ... I can't build a new motor every year! My neighborhood track is Mosport, which I think is considered a fairly fast track. And I still can't get into 5th [I know, I'm a slow driver]. The taller tires and gearing have added 6secs + to my my lap time at our first race last w/e. I have to admit the 60 series tires look really "right" on a vintage race 914, but looking good at the back isn't too much fun.

Gavin

Brant · 05-16-2006, 03:11 PM

wow... 6 seconds... ouch!

its an expensive proposition either way
and I know you mentioned cost being a part of it.
you can get 80% out of the less espensive gears
use a gear chart and start plotting.

pick your top speed along with tire specs and then work backwards.
usually with a few sacrifices you can do it for 1/2 of the cost of what optimum would be...

I'm switching to: F,J,O,S,V on my 914/6 but that took me a couple of years worth of savings to afford. should give me the best of both worlds.

John Rogers · 05-16-2006, 03:37 PM

When I had my transmission rebuilt with the lower gears, I had a GT limited slip installed and with new parts and labor it ended up at about $3,500 or so. We did find new gear sets as the used ones we looked at were not in the greatest shape and were still expensive as hell.

campbellcj · 05-16-2006, 10:42 PM

I have the A, GA, Ka (flipped ZD), Q, V setup as well. For longer/faster tracks you either need a lot of revs and/or taller tires to avoid being gearing limited on top speed, but overall it is a great setup. Night and day compared to the stock 914-4 gears with a small six, which is a total powerband mismatch.